Photo/Illutration Large cumulonimbus clouds over Yokohama, Kanagawa Prefecture, in 1989 (Asahi Shimbun file photo)

A recent study suggests that a temperature drop in Tokyo this spring may have been caused by the novel coronavirus pandemic halting public transportation and other socio-economic activities.

From April to May this year, when the nation was under a state of emergency issued by the central government, the temperature in the capital’s Chiyoda Ward was about 0.5 degree lower than normal.

Fumiaki Fujibe, a climatology expert who studied central Tokyo’s temperature readings from January to September, said the drop was likely due to the decrease of anthropogenic heat release, or heat caused by humans, as people drove less and businesses reduced their air conditioning use.

“Society as a whole cooled down, indeed,” said Fujibe, a project professor of the Department of Geography at Tokyo Metropolitan University.

Fujibe found in a previous study done in 2010 that the temperature in central Tokyo on weekends was 0.2 degree lower than weekdays.

The latest finding implies that socio-economic activities under the state of emergency were even more subdued than on an average weekend.

Fujibe said the “cooling” effects occurred outside the center of Tokyo as well.

The temperature dropped about 0.1 to 0.4 degree within a 75-km radius from Chiyoda Ward, according to the study.

The affected areas included Hachioji, western Tokyo, as well as Chichibu in neighboring Saitama Prefecture and Kamakura in Kanagawa Prefecture.

“The effects of anthropogenic heat release appear to be more widespread than expected,” Fujibe said.

Yuya Takane, a scientist who led similar research into Osaka's temperatures, said the fact that so many people voluntarily refrained from going out and doing other things under the pandemic “brought about almost the same effect as planting trees among buildings in some parts of the office district.”

Takane and a group of researchers at the National Institute of Advanced Industrial Science and Technology examined one large area, which they divided into an office district and a residential district. Based on data about the volume of people in each division, the researchers calculated the rates of air conditioning and electricity use, and estimated their effects on the temperature.

In the office district, where daily turnout decreased by 70 percent from normal, the researchers estimate that electricity usage dropped about 40 percent and the temperature dropped about 0.13 degree.

In the residential district, the researchers found that the number of people increased and electricity use slightly jumped, but the temperature was not affected much.  

Takane suggested that if the change in people's work routines becomes a permanent fixture, that could put a lasting chill on the amount of excess heat cities generate from human activities.  

“If teleworking becomes popular in central cities, it might lead to easing the urban heat-island phenomenon,” Takane said.

Takane's group also studied Osaka's temperatures in June 2019, when the G-20 Summit was held and traffic volume halved. At the time, the temperature in the capital of Osaka Prefecture dropped 0.05 degree.